ABSTRACT The goals of this proposal are to determine the type I interferon (IFN-I)-mediated antiviral gene program against SARS-CoV-2 infection and to develop novel broad-spectrum antiviral agents (BSAAs) for the treatment of COVID-19 and other emerging infectious diseases. There are no effective therapeutic agents currently available in the fight against the global COVID-19 pandemic, in which SARS-CoV-2 has infected millions of people in confirmed cases and caused hundreds of thousands of fatalities. Drugs that target a single virus, like the inhibitors of HIV reverse transcriptase and influenza neuraminidase, require a comprehensive understanding of the lifecycle and disease mechanisms of the virus, which makes development of these drugs necessarily time-consuming. Outbreaks of infection caused by novel emerging highly pathogenic viruses, including avian influenza, SARS, Ebola, Zika virus (ZIKV) and SARS-CoV-2, have become a major concern in the past two decades. We cannot rely on the traditional virus-specific drugs to treat diseases caused by these unpredictable emerging viruses. Therefore, it is extremely important to develop BSAAs effective against a range of viruses. My laboratory has been studying anti-viral innate immune responses, particularly the IFN-I signaling pathway and its downstream gene program, for the last 20 years. While the field has previously focused only on interferon-stimulated genes (ISGs), we have demonstrated that ISGs like cholesterol 25- hydroxylase (CH25H) and IFN-I downregulated genes like fatty acid synthase (FASN) both play important roles in limiting viral infection and replication. We have also identified multiple small molecules for use as BSAAs, including 25-hydroxycholersterol (25HC), the metabolic product of CH25H, and the FASN inhibitor C75. In addition, we have extensively studied host innate immune responses to coronaviral infection: we have published multiple papers that explain how the host IFN-I signal transduction pathway is activated in response to infection by coronaviruses like murine hepatitis virus (MHV) and how coronaviruses can suppress their host?s innate immune responses through the viral papain-like protease (PLpro). Most importantly, in our preliminary studies we found that 25HC and C75 both have strong inhibitory effects against SARS-CoV-2 infection. We hypothesize that the IFN-I-mediated antiviral gene program involves not only upregulation of antiviral ISGs but also downregulation of the host genes required for viral infection and replication. We further hypothesize that by identifying the IFN-I-mediated antiviral gene program against SARS-CoV-2, we will be able to develop novel antiviral agents to combat COVID-19 and other emerging threats. In this proposal, we will first determine the IFN-I gene program in innate immune response to SARS-CoV-2. We will also develop 25HC, 25HC analogs and FASN inhibitors as novel antiviral agents against SARS-CoV-2. We believe our studies will not only determine the IFN-I-mediated antiviral gene program in host innate immune response to SARS-CoV-2 infection but also develop BSAAs to treat COVID-19 and other emerging infectious diseases.